This invention relates to the production of uranium and more particularly to the recovery of uranium from a pregnant alkaline lixiviant by ion exchange adsorption.
Uranium is produced from uranium-bearing ores by various procedures which employ an alkaline lixiviant to leach the uranium from its accompanying gangue material. The leaching operation may be carried out in conjunction with surface milling operations in which uranium ore obtained by mining is crushed and blended prior to leaching, heap leaching of ore piles at the surface of the earth, or in-situ leaching in which the lixiviant is introduced into a subterranean ore deposit and then withdrawn to the surface. Regardless of the leaching operation employed, the pregnant lixiviant is then treated in order to recover the uranium therefrom. One conventional uranium recovery process involves passing the pregnant lixiviant over an anionic ion exchange resin and then eluting the resin with a suitable eluant to desorb the uranium from the resin. The resulting eluate is then treated to precipitate uranium therefrom to produce the familiar "yellowcake".
Procedures for the recovery of uranium from an alkaline lixiviant by anion exchange and subsequent elution are disclosed in U.S. Pat. Nos. 2,811,412 to Poirier, 2,841,468 to Wilson, and 2,982,605 to Mouret et al. Typically, the alkaline lixiviant contains alkali metal or ammonium carbonates or bicarbonates or mixtures thereof which function to solubilize hexavalent uranium in the ore as uranyl anionic complexes such as uranyl tricarbonate ions. The pH of the lixiviant normally is within the range of about 8 to 10. However, as disclosed by the aforementioned patents to Mouret et al. and Wilson, somewhat higher pH's are preferred in order to optimize adsorption of the uranium by the ion exchange resin. Thus, the patent to Mouret et al. teaches that the pH should range from 9.5 to 11.5 and preferably be equal to 10.5. The patent to Wilson discloses that the pH should be increased from a value of less than 10 to a value within a range of 10.8 to 11.8 in order to optimize the adsorption of uranium with respect to vanadium. Thus, Wilson discloses that at pH's of 6.9 and 8.9 the ion exchange resin preferentially adsorbs vanadium whereas at a higher pH of 11.2 the resin is selective with respect to uranium with very little vanadium being adsorbed.